On a railcar, wheeled trucks are provided toward and support opposite ends of a railcar body for movement over tracks. Each truck is operably connected to a bolster extending transverse to the centerline of railcar for supporting the railcar body. In the preponderance of freight cars, a pivotal connection is established between the bolster and railcar body by center bearing plates and bowls transversely centered on the car body underframe and the truck bolster. Accordingly, the truck is permitted to pivot on the center bearing plate under the car body. As the railcar moves between locations, the car body tends to adversely roll from side to side.
Attempts have been made to control the adverse roll of the railcar body through use of side bearings positioned on the truck bolster laterally outwardly of the center bearing plate. In this way, the car body is supported laterally outwardly of the center plate on the bolster, while permitting relative rotation between the car body and bolster to permit normal movement of the car along the tracks. A “gap style” side bearing has been known to be used on slower moving tank/hopper railcars. Conventional “gap style” side bearings include a metal, i.e. steel, block or pad accommodated within a pocket defined on the truck bolster. An upstanding box-like open-top casing, integrally formed with or secured, as by welding or the like, to the truck bolster defines the pocket and inhibits sliding movement of the metal block relative to the bolster. The pockets provided on the bolster can, and often do, differ in size relative to each other. A gap or vertical space is usually present between the upper surface of the “gap style” side bearing and the underside of the railcar body.
Under certain dynamic conditions, combined with lateral track irregularities, the railcar truck also tends to oscillate or “hunt” in a yaw-like manner beneath the car body. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they seek a centered position under the steering influence of the wheel conicity. As a result of such cyclic yawing, “hunting” can occur as the yawing becomes unstable due to lateral resonance developed between the car body and the truck. As will be appreciated, excessive “hunting” can result in premature wear of the wheeled truck components including the wheels, bolsters, and related equipment. Hunting can also furthermore cause damage to the lading being transported in the car body.
Track speeds of rail stock, including tank/hopper cars, continues to increase. Increased rail speeds translate into corresponding increases in the amount of yaw or hunting movements of the wheeled trucks. As will be appreciated, “gap style” side bearings cannot and do not limit hunting movements of the wheeled trucks. As such, the truck components including the wheels, bolsters, and related equipment tend to experience premature wear.
In an effort to improve upon the “gap style” side bearing, and so as to enhance truck hunting stability as well as car body lateral roll stability, constant contact side bearings are known in the art and typically include a base and cap. In some side bearing designs, the side bearing base has a cup-like configuration and is suitably secured to the upper surface of the bolster by suitable fasteners extending endwise through apertured lugs radically extending outwardly from the side bearing base. The apertured lugs extending from the side bearing base inhibit mounting such side bearings within the open-top pocket on the upper surface of the railcar bolster. The side bearing cap has an upper surface which is resiliently biased to contact and rub against an underside of the car body. The side bearing cap is free to vertically move relative to the base of the side bearing. Such constant contact side bearings furthermore includes a spring.
The spring for such side bearings can comprise either spring loaded steel elements or elastomeric blocks or a combination of both operably positioned between the side bearing base and the cap. The purpose of such spring is to resiliently urge the upper surface of the cap under a preload force and into frictional contact with an underside of the car body so as to resist relative sliding movement between the underside of the car body and the bolster as well as affecting the roll motion of the car body. One such elastomeric block is marketed and sold by the Assignee of the present invention under the trade name “TecsPak.”
The prior art also discloses a constant contact side bearing configured to fit or be accommodated within existing pockets on a truck bolster of a railcar. Like those mentioned above, these known constant contact side bearings include a base and a resiliently biased cap. As mentioned above, however, both the longitudinal and lateral sizes of the opening defined by the casing on the upper surface of the bolster can vary considerably between railcars. When the size of the opening or pocket defined by the casing is too large, the side bearing assembly base tends to slidably move within the pocket of the casing on the bolster thus losing or lessening the ability of the side bearing assembly to inhibit “hunting” movements.
Additionally, heat buildup in proximity to an elastomeric spring of constant contact side bearings is a serious concern. While advantageously producing an opposite torque acting to inhibit the yaw motion of the truck, the resulting friction between the side bearing and underside of the car body develops an excessive amount of heat. The repetitive cyclic compression of the elastomeric block coupled with high ambient temperatures, in which some railcars operate, further exacerbate spring deformation. As will be appreciated, such heat buildup often causes the elastomeric block to soften/deform, thus, significantly reducing the ability of the side bearing to apply a proper preload force whereby decreasing vertical suspension characteristics of the side bearing resulting in increased hunting.
Thus, there is a continuing need for a constant contact railcar side bearing assembly designed to fit within bolster pockets which are both laterally and longitudinally greater in cross-sectional size that the cross-sectional size of the side bearing assembly adapted to fit therewithin.